Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F6/00—Post-polymerisation treatments
  • C08F6/04—Fractionation
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F8/00—Chemical modification by after-treatment
  • C08F8/50—Partial depolymerisation
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J3/00—Processes of treating or compounding macromolecular substances
  • C08J3/28—Treatment by wave energy or particle radiation
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J2323/00—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers
  • C08J2323/02—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers not modified by chemical after treatment
  • C08J2323/04—Homopolymers or copolymers of ethene
  • C08J2323/06—Polyethene
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L23/00—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers
  • C08L23/02—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers not modified by chemical after-treatment
  • C08L23/04—Homopolymers or copolymers of ethene
  • C08L23/06—Polyethene
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S526/00—Synthetic resins or natural rubbers -- part of the class 520 series
  • Y10S526/914—Polymer degradation

Definitions

• the conventional low pressure polyethylene is distinguished from the high pressure polymer by its higher melting point, its superior stiffness and its relatively high molecular weight which permits fabrication of articles of higher tensile, bending and bursting strengths.
• These lower pressure polymers however, still suffer from the deficiency of a high melt viscosity which limits their field of utility in certain respects, especially their working properties.
• the complicated branched structure of the high pressure polymer is particularly responsible for the low melting point (about 110 C.) and for a wide molecular weight distribution which is characterized by a ll'l zll'l (weight average molecular weightznumber average molecular weight) ratio of more than 6 or 8:1 and sometimes even as high as :1, whereas the normal ratio for a vinyl-type polymer such as polystyrene has been found to be approximately 2. (The significance of the 1 1, 11?
• the low pressure, low temperature polyethylenes consist of essentially linear macromolecules which may have a few long branches ,(5 or 6 per molecule) but do not have any short branches. This explains in a sufliciently satisfactory manner the higher degree of crystallinity, the higher density, higher melting point, lower moisture permeability and higher resistance to solvents.
• the present invention relates to the provision of a 15 novel polymer of ethylene having particularly valuable characteristics making it especially suited for molding, extrusion, casting and spinning. More particularly, the present invention relates to a novel polymer of ethylene characterized by a high melting point, a high average 20 molecular weight, a high uniformity of molecular weight, and a relationship between tensile strength (flexural and impact) and melt viscosity which is different from and superior to that of all other polyethylenes heretofore known. i
• Ethylene has heretofore been polymerized through th use of high pressure to produce a white solid product having a generally greasy feel.
• a more recent polymerization technique which is described and claimed in my cope'nding application Serial No. 550,761, filed December 2, 1955, now abandoned, utilizes lower pressures and more moderate temperatures, the polymerization being advanced by means of special catalysts. The prodnot so obtained is superior in many respects to that derived by the high pressure method.
• the following table compares the properties of the products obtained by these methods:
• melt viscosity is found as follows:
• the low molecular weight fraction 4 By way of explanation, the number average molecular weight, fi of a polymer is defined by the equation 77 ff(M)MdM ff dM or in more simple arithmetical terms, the number average molecular weight of a sample of a mixture containing various amounts of individual species of different molecular weights is found by multiplying the number of molecules of a given species by its individual molecular weight and finding the sum of all these products to give a numerator which divided by the total number of molecules in the sample, the quotient being E
• the weight average molecular weight, H of a polymer is defined by the equation or in more simple arithmetical terms, the weight average molecular weight of a sample of a mixture containing various amounts of individual species of different molecular weights is found by multiplying the number of molecules for a given species by the square of their individual molecular weight and finding the sum of all these products to give a numerator which is divided by the sum of a series of
• M is obtained by all those methods which count the individual molecules in a solution of the sample such as the direct measurement of the osmotic pressure, the vapor-pressure lowering, the boiling-point elevation, the melting point lowering or the determination of end-groups;
• IVI is obtained experimentally by measuring the light-scattering (turbidity) of the macromolecular solution or by the combination of sedimentation and dilfusion.
• Another object of the invention is to provide procedures whereby such novel polyethylenes are obtained.
• polyethylene compositions of improved properties can also be obtained by degrading a polyethylene having a wide molecular weight range so that a polyethylene having a reduced molecular weight range is obtained.
• the novel polyethylenes thus obtained though of a somewhat lower weight average molecular weight than the starting material have the same melting point and other desirable properties and in addition have certain beneficial properties not exhibited by the starting material itself.
• the fractionation procedure is effected by dissolving polyethylene in xylene at elevated temperature.
• An organic material inert with respect to the polyethylene and the xylene, but soluble in or miscible with the xylene, is then added in increments with slight cooling.
• a first fraction is obtained of very high molecular weight, this fraction being distinctly more uniform-than the starting material but nevertheless having a higher molecular weight and consequently also a higher melt viscosity.
• the organic liquid is then added in further increments with formation of a cloudy precipitate. Cooling aids in settling out of the precipitate which can then be separated by filtration or centrifugation, the residual solution being further diluted for separation of further fractions.
• the precipitant can be any substance soluble in or miscible with the polyethylene solvent. Suitable materials include aliphatic hydrocarbons, alcohols, ethers, and the like. Normally solid substances which liquefy or dissolve in the solvent under the ambient conditions may also be employed 'as precipitants.
• the degradation of heterogeneous polyethylene to produce a composition of narrow molecular weight range can be effected in solutionby means of ultrasonic irradiation.
• Example I 1.5 grams of TiCl, were dissolved in 40 ml. of dry heptane and added to a flask provided with a mercury sealed stirrer and a nitrogen inlet tube to provide a dry nitrogen blanket. 0.6 gram of aluminum triethyl dissolved in an additional 40 ml. of heptane was added and the mixture stirred. The black suspension which formed was maintained in colloidal condition by stirring and dry oxygen-free ethylene was bubbled into the flask continuously with gradual formation of a dark colored polyethylene. After about 24 hours, absorption and polymerization of ethylene ceased.
• the soft solid in the flask was treated with methanolic HCl, transferred to a filter, washed successively with dilute methanolic HCl, methanol, and water yielding a white material. 0n drying at 80 C. under vacuum there was obtained 40 grams of a white powder soluble in xylene at elevated temperature.
• Example II 1 gram of the dry polyethylene obtained in Example I was dissolved in 50 ml. of xylene at 95 C. Hot propanol was added gradually with vigorous stirring while permitting the solution to cool slightly. The dropwise addition of the propanol first caused a slight haze and then a gelatinous precipitate which was rendered fluilfy and more easily filterable by reducing the temperature of the solution to 90 C. This first precipitate was filtered oif and after drying in vacuum yielded 0.21 gram of a white fluffy powder.
• the new polyethylenes of the present invention can also be prepared by ultrasonic irradiation as shown in the following example:
• Example III 2 grams of the polyethylene obtained in Example I were dissolved in 100 ml. of xylene at C. A clear homogeneous solution was obtained which permitted the application of several experimental methods for the characterization of the dissolved polymer. Osmotic measurement gave a number average molecular weight of 70,000; light scattering measurements led to a weight average molecular weight of 560,000; the intrinsic viacosity was 1.36 whereas the melt viscosity of the polymer itself was 5.8Xl0 poises.
• melt viscosities of these new materials are below poises at 150' C. and often range between 10' and 10 poises, or even lower, while the molecular weighfis about 60,000.
• the process for fractionating polyethylene having a ratio of weight average molecular weight to number average molecular weight of less than about 4, which comprises dissolving in liquid xylene polyethylene having a weight average molecular weight to number average molecular weight ratio greater than about 4, a number average molecular weight in excess of about 25,000 and a melting point in excess of about 125 0, adding to said solution a volatile liquid non-solvent for said polyethylene which liquid is soluble in xylene, said liquid being added in quantity suflicient to precipitate a first fraction of said polyethylene, cooling the solution and separating the precipitated first fraction, adding further liquid to the solution to precipitate a second fraction of polyethylene while leaving a third fraction in said solution, cooling said solution and separating said second traction, and sep- 8 arately heating said precipitated polyethylene fractions to drive 01! any xylene and volatile liquid non-solvent adhering thereto.
• the process which comprises forming a solution of polyethylene having a weight average molecular weight to number average molecular weight ratio greater than about 4, a number average molecular weight in excess of about 25,000 and a melting point in excess of about C., subjecting said solution to ultra-sonic irradiation whereby polyethylene molecules of high molecular weight are broken down, and recovering the polyethylene from said solution.

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• Chemical & Material Sciences (AREA)
• Health & Medical Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Medicinal Chemistry (AREA)
• Polymers & Plastics (AREA)
• Organic Chemistry (AREA)
• General Chemical & Material Sciences (AREA)
• Addition Polymer Or Copolymer, Post-Treatments, Or Chemical Modifications (AREA)
• Manufacture Of Macromolecular Shaped Articles (AREA)
• Processes Of Treating Macromolecular Substances (AREA)

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Citations (8)

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• 0
  • IT IT568134D patent/IT568134A/it unknown
  • DE DENDAT1068891D patent/DE1068891B/de active Pending
• 1955
  • 1955-12-27 US US555292A patent/US2910460A/en not_active Expired - Lifetime
• 1956
  • 1956-12-26 FR FR728357A patent/FR1320001A/fr not_active Expired
  • 1956-12-27 GB GB39371/56A patent/GB848753A/en not_active Expired

Patent Citations (8)

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